Compose an email with an inline image

Some time ago I managed to force Mail to always put attachments at the end of the email. Now I would like to revert this setting.

As I don't find anything in the GUI (preferences) I suppose that I changed some preferences with the terminal.

I see that I have AttachAtEnd=1 in my preferences

> defaults read com.apple.mail  | grep AttachAtEnd
AttachAtEnd = 1;

But it seems that I am not able to change it

> defaults write com.apple.com AttachAtEnd -bool No
> defaults read com.apple.mail  | grep AttachAtEnd
AttachAtEnd = 1;

or

> defaults delete com.apple.com AttachAtEnd
> defaults read com.apple.mail  | grep AttachAtEnd
AttachAtEnd = 1;

How can I remove it?